Extract & refactor `kitchen list` subcommand.
Extract & refactor `kitchen console` subcommand.
Extract & refactor `kitchen sink` subcommand.
Small update to `kitchen version` subcommand implementation.
Extract & refactor `kitchen login` subcommand.
Extract & refactor `kitchen diagnose` subcommand.
Extract & refactor `kitchen test` subcommand.
Extract & refactor `kitchen ACTION` subcommands.
Extract & refactor `kitchen driver discover` subcommand.
Remove unused code from CLI-related files.
Merge pull request #302 from test-kitchen/cli-refactoring

CLI refactoring to remove logic from cli.rb